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The Sun's Radiative Zone

The Sun's radiative zone is the section of the solar
interior between the innermost core and
the outer convective
zone. In the radiative zone, energy generated by nuclear
fusion in the core moves outward as electromagnetic
radiation. In other words, the energy is conveyed by photons.
When the energy reaches the top of the radiative zone, it begins to move
in a different fashion in the convective zone. In the convective zone, heat
and energy are carried outward along with matter in swirling flows called
convection cells. This motion is similar to the roiling flows seen in a pot
of boiling water.

The inner parts of the Sun (core and radiative
zone) spin
differently than the outer layers (convective zone). The boundary between
these two types of rotation, which lies between the radiative and convective
zones, is called the tachocline.

Many other stars also have radiative zones. The Sun's radiative zone extends
from the core outward to about 70% of the Sun's radius. In a smaller (than
the Sun) star that is cooler than our Sun, the convective zone tends to be
larger, extending deeper into the star's interior. Thus the radiative zone
tends to be smaller. In very small, cool stars the convective zone may reach
all the way to the star's core, and there may be no radiative zone at all.
In a larger (than the Sun) star with a higher temperature, the radiative zone
tends to be larger and the convective zone smaller. Especially large, hot stars
may not have a convective zone at all - their radiative zone may extend all
the way from the core to the star's surface.

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